Controlling the Hierarchical Assembly of DNA-Based Hexagonal Microstructures

This paper discusses the controlled morphology of hierarchical liquid crystalline DNA assemblies. Through a process of heating and slow cooling, double-stranded DNAs (dsDNAs) having 23 complementary bases and two base overhangs (a pair of 25mer oligonucleotides) spontaneously assemble into micro-sized hexagonal platelets in a solution containing poly(ethylene glycol) (PEG) and salt. Remarkably, the addition of a shorter dsDNA with AA/TT overhangs (a pair of 18mer oligonucleotides) to a PEG-salt solution of 25mer DNA with AA/TT overhangs results in the formation of molecular tubes, each with a central blockage. In contrast, the addition of 18mer DNA with GG/CC overhangs leads to the formation of hexagonal frames from hexagonal platelets. In the assemblies, 18mer DNA is more predominant at the edges, while the central nuclei are composed of 25mer DNA. X-ray scattering measurements reveal that both molecular tubes and hexagonal frames form hexagonal columnar liquid crystalline assemblies. These self-assemblies are thought to result from depletion attraction due to PEG and end-to-end stacking between dsDNA overhangs. Differences in the melting temperatures between longer and shorter dsDNAs enable the stepwise formation of hierarchical assemblies, while variations in overhang sequences modulate the overall morphology by altering the growth direction of the assemblies.